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Temperature changes

Climate projections displayed in this map represent the average of the maximum air temperature (degrees F) for June, July, and August for the years 2010-2080 using current data, or one of two IPCC greenhouse gas concentration scenarios: a moderate emissions scenario (RCP 4.5) and a high emissions scenario (RCP 8.5). These datasets are intended to represent typical summer temperatures in the decade indicated. The range of temperatures shown correspond to approximately 70 - 90 °F or 20 - 35 °C. Climate projections were developed by a University of Massachusetts Amherst team for the Northeast region to evaluate the potential effects of climate change on wildlife habitat and ecological integrity from 2010 to 2080. Data courtesy of the North Atlantic Landscape Conservation Cooperative.

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Stressors

Temperature changes

Annual and Seasonal Temperature Changes
The Earth’s climate is warming. Global average annual temperatures have increased by 1.5°F since 1895, and the vast majority of this increase has occurred since 1980. The northeast United States has experienced an increase in annual temperatures of 1.6°F over the last century. Warming has been occurring during all seasons, but has been greatest during winter (0.24°F/decade). Warming is also greatest at higher latitudes, elevations, and inland from the Atlantic coast.

Future climate projections consistently show continued warming over the 21st century across Massachusetts and the entire New England region. All climate models agree that the warming trend will continue over the coming decades with high emission scenarios giving the greatest warming. However, for a given emissions scenario, the exact magnitude of warming varies slightly depending on the models used and their structure. Massachusetts is projected to see average temperature increases that exceed the global average, with potential warming of around 5°F annually by mid-century under a high emissions scenario. Model projections of future seasonal changes generally suggest winter will continue to show the greatest amounts of warming with increases up to 5°F by mid-century.

Extreme Temperature Events
Extreme temperatures in the form of heatwaves may become more frequent, more intense, and last longer. Extreme high temperature events are on the rise globally. Warmer night-time temperatures are driving this overall trend with fewer cold nights and more warm nights. However, there is evidence of a “warming hole” over the past half century across the eastern U.S., where the number of warm days has been either constant or slightly decreasing and the number of cool days increasing.

Heatwave intensity, frequency, and duration are expected to increase over the U.S. in the 21st century. Fewer cold days and nights, and more warm days and nights are also expected over the 21st century. Minimum temperatures (daily lows, temperature on the coldest day of the year) are rising, and are expected to continue to rise faster than maximum temperatures (daily highs, temperature on the warmest day of the year). The highest elevations in Massachusetts and the greater New England region are likely to see large increases in daily summer maximum and minimum temperatures in the future.

Extreme cold winter temperatures in Massachusetts and the Northeast region observed during recent years are thought to be the result of rapid warming in the Arctic, which influences the strength and meandering of the jet stream. These anomalous cold temperatures were the exception as the rest of the world experienced record high temperatures. Studies of these extreme temperature events are an emerging area of climate research. Recent research suggests that it is likely that North America will experience additional extreme winter temperatures, though they are expected to vary in intensity and frequency over time.

Changes in the Growing Season
Growing degree days and the overall growing season length is generally defined as the number of days between the dates of the last spring frost and the first fall frost. Frosts occur when the minimum daily temperature drops below freezing (32 °F). Between 1895 and 2011, there has been a strong increase in growing degree days in Massachusetts and the greater New England region due to shorter winters and longer summers. The growing season has lengthened in Massachusetts by approximately 10 days since the 1960s. The average date of the last frost in spring has been getting earlier each year, and the date of the first frost in fall has been getting later across New England.

Future climate projections using a high emission scenario show continued lengthening of the frost-free season across New England by at least 19 days by the year 2055, and as much as 1 – 2 months by the end of the century, depending on the emissions scenario.

9. Kunkel, K. E. 2013. Regional climate trends and scenarios for the US National Climate Assessment. US Department of Commerce, National Oceanic and Atmospheric Administration, National Environmental Satellite, Data, and Information Service.